Even though there are significant advancements made in the ultrasound scanning technologies for scanning biological objects to carry out medical image and diagnostic tasks, there are still technical difficulties caused by signal interferences that lead to image degradations.
Specifically, during the transmitting period a high voltage burst pulse, e.g., a 100 Volt burst pulse, is applied to excite the transducer in an ultrasound imaging system to project ultrasound signals into a biological object to perform an image scanning operation. Then the echo signal reflected back from the biological object is received and amplified to construct the tissue image or to detect the blood velocity by applying an analysis using the principle of Doppler effect. However, the echoed signals received from burst to burst are modulated due to the interferences caused by the switching operations of the high voltage power supply interference, e.g., the outgoing burst signals are interrupted by the switching noises thus affecting the echo signals. A two-dimensional scanned image reflected back from the biological tissues thus presents an interference pattern due to these interferences. Furthermore, the interferences also cause the Doppler spectrum to present extra inter-modulation tones. The quality of scanned data and the images constructed from the scanned data are therefore degraded.
Referring to FIG. 1 for a conventional ultrasound system that includes transducer 15 for sending the burst acoustic wave to the body and also receive the echo from the tissue. The ultrasound system further includes a front-end beam former 20 to generate a delay profile of ultrasound waves to focus the beam for both transmitting the ultrasound waves into the biological objects and for receiving the echo signal back to the transducer 15. A high voltage generator 35 receives an AC input from a power source to generate low voltage for the system supply and high voltage for the transducer excitation. Typically, a high voltage for the piezo ceramic transducer is from 30 to 200 volts. The ultrasound system further includes a back end processor 25 to receive signals from the front end processor 20 and also receives user commands from a user interface 40 to perform various back end processes and for generating images for displaying on a display monitor 30.
FIG. 2 is a functional block diagram for showing a conventional high voltage generator for generating the high voltage. The high voltage generator includes an isolation transformer 45 that received an AC input voltage that can be either 110 volts or 220 volts AC input. The isolation transformer 45 performs a step down process to provide a low voltage AC output for the low voltage linear DC regulator. Additionally, the isolation transformer 45 further carried out a step up process to provide output for the high voltage linear regulator. The high and low AC voltages generated from the isolation transformer 45 are processed by a linear regulator 50 to convert the AC to DC voltages for both low voltage i.e. +3.3, +5, +12 V and the high voltage i.e. 150V. The high voltage output is provided to the front-end beam former that includes transmitting pulser for carrying out a transducer excitation function. Since the high voltage generator does not perform a switching function, the high voltage generator 50 does not generate and emit switching noises. The isolation transformer commonly implemented in an ultrasound system is heavy and bulky and also are operated with very low efficiency (e.g. less than 60%).
Referring to FIG. 3 for another conventional approach implemented in a high voltage generator that includes a main switching power supply 55 to receive an AC input and then apply a DC to DC switcher 60 to generate the high voltage for the front end pulser. The DC-to-DC switcher 60 can be optionally implemented as a conventional power supply with switcher followed by a linear regulator. In a conventional system, the common practice is for the DC-to-DC switcher 60 to employ an internal clock that is free running in generating the switching frequency for the high voltage output. Such configuration and circuit implementation however generate a technical difficulty that the DC voltages generated from the free running switching clock create incoherent interferences that affect the receiving echo in many aspects of the system operations. First of all the internal free-running clock generates signals that beat with the system clock. The signals from the free-running switching clock also modulate the wave transmissions emitted from the front-end pulser. Furthermore, the free-running switching clock further interferes with the electric circuits in the front-end receiving beam former and in the transducer shielding. These interferences further degrade the scanned images due to the impacts that these interferences have on the patterns of the two-dimensional images or the inter-mod tones on the Doppler spectrum.
As shown in FIG. 2, in order to avoid the interference problems, the conventional ultrasound imaging systems use Linear Power regulator 50 with step up transformer to generate the High Voltage for the Doppler Ultrasound system. The transformer used in the high voltage linear regulator is heavy and bulky and not suitable for a portable unit. When people use conventional switching mode power Supply for the ultrasound system to improve the efficiency in the portable ultrasound unit, the system usually requires a very significant shielding and a special routing for ground returns to prevent the in-coherent switching noise from getting into the transducer and front end circuitry during receiving. With the latest DC-DC switching technique available in the market, the switching frequency can go up to 400 KHz or higher, and creates various strong harmonics. This new technology increases the power efficiency, reduce the component size, but will create a big challenge in shielding the interference from the switching frequency and its harmonics. The problem is worse in the highly sensitive all digital front end with color Doppler, pulse (PW) and continuous wave (CW) Doppler functions.
Therefore, the conventional ultrasound systems employed to obtain Doppler and image signals are either bulky or become very vulnerable to the interferences by the high voltage switching noises. These interference noises can affect the signals receptions either through the radiation propagated in the system or through the conductive path. Such problems are especially pronounced in the portable color Doppler units due to the very limit space of such device. Special designs to provide layout to shield such interferences become a highly difficult task. In a conventional system, the unit still remains as a cart unit because the linear regulator is still implemented with bulky and heavy shield to prevent interferences. The portability of a color Doppler unit is therefore greatly limited.
For these reasons, a need still exists for those of ordinary skill in the art to provide an improved method and system for medical image scanning operation by applying an ultrasound system. Specifically, it is desirable to provide an improved system design to minimize the effects of signal interferences caused by power supply switching noises.